Designing Spray Booths by Applying the Right Airflow Design

Q: We are in the market for new booths for our spray coating applications. What are some features and considerations we should be looking at?

A: Spray booth solutions are varied. Whether you need a downdraft airflow design, crossdraft, semidowndraft or modified downdraft, you need to choose the right one. Many engineers consider a number of key performance objectives to arrive at the best airflow option for your operations:

• Optimizing booth size
• Boosting production flow
• Enhancing spray quality and finish
• Ensuring regulatory compliance
• Reducing cost of booth operations

Here’s a quick guide to each airflow design and how they operate to deliver the quality of finish you desire:

Crossdraft Spray Booth: These booths are designed to handle a wide variety of parts and sizes. The term crossdraft refers to how the air travels through the booth. In this case, horizontally along the “cross section” of the booth. The air passes from the front of the booth (sometimes through supply filters) and then horizontally toward the booth’s rear exhaust chamber. This horizontal direction causes air to flow uniformly over the painted part as it enters the exhaust filter chamber (which incorporates the exhaust filters). The result — air is filtered from any paint overspray as it passes through the filters. The filtered air is pulled by the exhaust fan through the exhaust filters and exhaust duct system as it is discharged into the atmosphere.

Downdraft Spray Booth: These booths are also designed to handle a wide variety of parts and sizes. The term downdraft refers to the direction of air travel in the booth. In this case, in a downward movement from the ceiling to the floor of the booth. Supply air enters the top supply plenum where filters are located in the ceiling and then passes over the part as it moves toward the booth floor. Overspray is directed to the grating that is over a pit in the floor and then through exhaust filters, typically located beneath the grating. The overspray passes through the filters and is removed from the air stream as it is drawn by the exhaust fan and ductwork system to discharge cleanly into the atmosphere.

Semidowndraft Spray Booth: This booth design combines the benefits of crossdraft with downdraft to achieve higher quality finish requirements. Using the design principles of downdraft and crossdraft, the air is introduced in a ceiling supply plenum located at the front of the booth. The air moves down and back toward the rear exhaust plenum at the opposite end of the booth and located closer to the floor. The air has a semidowndraft movement and passes over the part in a downward and then horizontal movement as it approaches the rear exhaust plenum. The exhaust chamber and filters are similar to crossdraft, so air is filtered from paint overspray as it passes through the filters. Clean air is pulled by the exhaust fan through these filters and exhaust duct system and discharged into the atmosphere.

Modified Downdraft Spray Booth: Large equipment applications need special booth designs, where multiple spraying operations are required. Modified downdraft refers to a downward movement of air, from ceiling to floor. Air enters the top supply plenum, where filters are located in the ceiling, then passes over the part as it moves toward the booth floor. Airflow is “modified” as the exhaust filters and plenums are located along the length of the booth near the floor. Unlike a downdraft booth that requires a pit in the floor with grating, this modified airflow does not require a pit, but still allows the air to travel from ceiling to floor by diverting air to the side exhaust plenums. As overspray is directed to these side plenums, overspray passes through the filters and is removed from the air stream as it’s drawn by the exhaust fan and ductwork system to discharge cleanly into the atmosphere.

---

Bob Hauck is vice president at Spray Systems. Visit spraysystems.com